Add LED descriptions to documentation.

README.md

@@ -144,6 +144,16 @@ The sniffer can provide additional information. For every packet, you can displa
 Copy the provided script to the appropriate directory (it can be found in `About Wireshark -> Folders -> Personal Lua Plugins`).
 If the directory is not displayed, ensure that the Wireshark was built with Lua support. This can be checked in the `About Wireshark` window.
 
+## Indicator LEDs
+
+The firmware uses the following LEDs to indicate operation:
+* PCA10056:
+    - LED1 - toggled continuously
+    - LED4 - toggled when new frame is received
+* PCA10059:
+    - green LD1 - toggled continuously
+    - blue LD2 - toggled when new frame is received
+
 ## Troubleshooting
 
 See the sections below for the description of several known issues with the respective workarounds.